1. Field of Use
This invention relates to data processing and more particularly to microprocessor chips.
2. Background
With the significant and rapid changes in technology, manufacturers of minicomputer systems find it necessary to upgrade their systems more frequently than before. The upgrading process has taken the form of introducing new systems or retrofiting of old systems or a combination of both.
The introduction of new microprocessor chip designs has been a significant driving force in computer system upgrading. Constantly, chip manufacturers as well as some minicomputer system manufacturers are designing new chips that offer increased functionality and higher speeds. These new faster chips are in turn being made the basis of new system designs.
The chip manufacturers and computer system manufacturers have recongnized and continue to recognize the importance of compatibility between microprocessors. For example, several manufacturers of 32-bit microprocessors introduced in 1983 have emphasized their capability run software written for microprocessors that had preceded them.
For the most part, compatibility in such instances has been achieved by emulation through microprogramming, by modifying portions of the operating system, or by utilizing similar architectures. While such compatibility has been achieved, these chips are still able to provide only downward software compatibility. This means that the same software written for 8 or 16-bit microprocessor chips can be executed on 32-bit chips.
However, as chip designs continue to evolve minicomputer manufacturers still will be required to maintain inventories of those different microprocessor chips utilized in new and old minicomputer designs. That is, downward software compatibility does not require downward hardware compatibility.
In fact, the opposite is usually the case. This means that in order for an older minicomputer system to take advantage of a new chip, it is necessary to redesign or retrofit the system to accept the new chip notwithstanding the compatibilities in chip pin assignments. The reason is that the new chip besides being faster usually includes new functionality which enhances its marketability. This can prove costly in terms of both equipment maintenance and inventory.
Accordingly, it is a primary object of the present invention to provide an improved design methodology and apparatus for providing compatibility in chip designs.
It is a more specific object of the present invention to provide a chip which is usable in both new and older systems without requiring changes to be made to such older systems.